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BACKGROUND The carbon sequestration potential is affected by cropping system and management practices, but soil organic carbon ( SOC) sequestration potential under fertilizations remains unclear in north China. This study examined SOC change, total C input to soil and, via integration of these estimates over years, carbon sequestration efficiency ( CSE, the ratio of SOC change over C input) under no fertilization (control), chemical nitrogen fertilizer alone (N) or combined with phosphorus and potassium fertilizers ( NP, NK, PK and NPK), or chemical fertilizers combined with low or high (1.5×) manure input ( NPKM and 1. 5NPKM). RESULTS Results showed that, as compared with the initial condition, SOC content increased by 0.03, 0.06, 0.05, 0.09, 0.16, 0.26, 0.47 and 0.68 Mg C ha−1 year−1 under control, N, NK, PK, NP, NPK, NPKM and 1. 5NPKM treatments respectively. Correspondingly, the C inputs of wheat and maize were 1.24, 1.34, 1.55, 1.33, 2.72, 2.96, 2.97 and 3.15 Mg ha−1 year−1 respectively. The long-term fertilization-induced CSE showed that about 11% of the gross C input was transformed into SOC pool. CONCLUSION Overall, this study demonstrated that decade-long manure input combined with chemical fertilizers can maintain high crop yield and lead to SOC sequestration in north China. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Modern intensive agricultural practices, particularly the use of nitrogen fertilizers, have accelerated soil acidification on a global scale. The soil pH buffering capacity (pHBC) is often used to quantify the soil acidification rate. Calcareous soils have relatively higher pH and pHBC, reflecting the presence of carbonate minerals; however, the impact of long-term fertilization treatment on pH and pHBC is poorly understood for calcareous soils. Here, calcareous soil samples (0–20 cm) were collected from fields receiving six different fertilization treatments for 22 years: control (CK, unfertilized but planted); nitrogen (N); nitrogen and phosphorus (NP); nitrogen, phosphorus and potassium (NPK); combined manure and NPK (NPKM); and combined corn-stover and NPK (NPKS). Both pH and pHBC significantly decreased for all treatments relative to CK. NPKS treatment had the lowest soil pH. Compared with CK, the soil pHBC decreased 5.7 to 17.3% under different treatments. The calcium carbonate (CaCO3) content was significantly reduced by fertilization treatments, with a maximum decrease under the NPKS treatment. Structural equation model (SEM) analysis revealed that calcium carbonate and soil organic matter (SOM) made important contributions to effective cation exchangeable capacity (ECEC). Soil pHBC was directly controlled by ECEC, while CaCO3and SOM indirectly contributed to the pHBC through ECEC. These results indicated that NPKS treatment induces more severe soil acidification, reflecting the higher H+input and lower pHBC under this treatment. [ABSTRACT FROM PUBLISHER]

Nutrient availability and plant diversity are two important factors determining crop productivity in agricultural ecosystems, but little is known about the underlying mechanisms shaping microbial communities and their regulatory roles in soil biological activity and function. Here, we explored the impacts of fertilization regimes and crop rotations on soil physicochemical properties, crop yield and bacterial and fungal community structures in a 26-year field experiment. The critical determinants for regulating soil enzyme activity profiles involved in carbon (C), nitrogen (N) and phosphorus (P) cycling were identified by the partial least squares path model (PLS-PM). Long-term inorganic or organic fertilization significantly increased soil total N by 27%–77% and crop yield by 237%–419% and decreased soil pH by an average of 0.4 units when compared with non-fertilized control. Soil bacteria were more sensitive than fungi to the fertilization practices. Nutrient additions enriched copiotrophic taxa affiliated to the Pseudomonadaceae and Cytophagaceae bacterial families, but reduced some Acidobacteria such as subgroup 4 RB41, which was the most sensitive biomarker responding to no fertilization. Conversely, fungi were more active in response to crop conversion from wheat-maize to wheat-soybean rotation, leading to a 3-fold enhancement of an unclassified Sordariomycetes family in soybean-based rotation. PLS-PM revealed that fertilization-induced increases in soil enzyme activities were regulated by the bacterial community, while plant-driven alterations in yield, organic C input and soil aggregate-size distribution played an important role for fungal development, which, however, had no significant link to soil enzyme activity profiles. Our results suggest that different response patterns of soil bacteria and fungi to agricultural practices might have consequences for ecosystem function. [ABSTRACT FROM AUTHOR]

Soil microbes and nematodes are important components of soil biota that strongly affect agricultural productivity and sustainability. Currently, our knowledge on the response of soil biota to agricultural management is restricted. This study aimed to identify the relationship between microbial and nematode communities and explore the resource path that flows within the soil micro-food web under different fertilization practices in a winter-wheat/summer-maize rotation system. The experiment was a randomized complete block design with three replicates for each treatment that included unfertilized control; inorganic N, P and K fertilizer (NPK); NPK plus manure; and NPK plus maize straw. Soil samples were taken at a 0–20 cm depth when wheat and maize were harvested. The results showed that organic manure or maize straw combined with NPK fertilizers had positive effects on the soil microbial and nematode communities. For example, the incorporation of straw increased the fungal biomass. Long-term inorganic fertilization might restrain nematode biomass accumulation especially in fungivorous nematodes. The analysis of the metabolic footprints of nematodes suggested that the incorporation of straw could enhance the carbon resource flow into the soil food web by enhancing nematode biomass. Structural equation modeling analysis suggested that the bottom–up control from the microbial community to the nematode community was more obvious in the wheat season in comparison with the maize season. In addition, a relatively stronger predation relationship was found between omnivores–predators and bacterivores rather than fungivores. Our study suggests that organic management combined with NPK fertilization could effectively enhance the association between microbial and nematode communities, while a crop rotation system with maize may have a negative influence on the structure of the soil micro-food web. [ABSTRACT FROM AUTHOR]

Abstract: Soil degradation and water pollution could have resulted from inappropriate phosphorus (P) supply. Soil Olsen P is generally a good indicator to estimate bio-availability of P and environmental risk in alkaline soil. The change in Olsen P is always strongly affected by soil organic carbon (SOC) when different forms of inorganic and/or organic P are applied to farmlands with chemical fertilizer and/or manure. We related soil Olsen P to apparent P balance (APB) and SOC in alkaline soils at three 15-year (1991–2005) fertilization sites of northern China. Six treatments were examined: unfertilized control, chemical nitrogen (N), chemical NP, chemical N plus potassium (NK), chemical NPK, and chemical NPK plus animal manure (NPKM, same total N but 20–80% more P). Compared to the initial Olsen P in 1990, after 15years Olsen P was increased under P fertilization but decreased under no-P fertilization. At the three 15-year fertilization sites, annual mean Olsen P was 4.9–12.3 times higher under NPKM, 1.9–2.8 times higher under NP and NPK, but only 28.3–84.8% under Control, N and NK. Annual mean percentage of Olsen P to total P was higher under NPKM (4.6–8.1%) than under other five fertilizations (0.4–2.9%). Change in Olsen P significantly positively correlated with accumulated APB under all fertilizations (r 2 =0.10–0.31, P <0.05). At these three sites, Olsen P could be increased by 5.2, 5.8 and 12.1% respectively under NP, NPK and NPKM when 1kgP/ha was in surplus, meanwhile Olsen P was decreased by 2.1, 4.0 and 6.4% under Control, N and NK when 1kgP/ha was in deficit. Significantly higher SOC accumulation was under NPKM than under other five fertilizations when calculated by the same unit of P input. The combination of chemical P and manure P with organic C input is a better strategy to increase soil Olsen P and SOC accumulation on farmland with maize–wheat rotation in northern China. [Copyright &y& Elsevier]

Highlights: [•] Long-term field research proved that manure application with chemical fertilizer improved the nitrogen use efficiency (NUE) of wheat–corn rotation system the most especially in acid soil. [•] Phosphorus is found to be another important factor to improve NUE up to 40–60% if soil is P deficient. [•] Between the rotation crops, both grain yield and NUE of wheat were determined more responsive to P fertilization, and that for corn were more responsive to manure application. [Copyright &y& Elsevier]

The decomposition processes of crop residues, which represent the largest organic carbon input in agricultural ecosystems, are determined by soil microbes. However, the impact of different long-term fertilization practices on residue decomposition has not been clearly established. In this study, a microcosm experiment using 13C-labeled maize residues and high-throughput sequencing was performed to investigate bacterial and fungal microbes utilizing straw-derived carbon in soils under separate regimes of long-term fertilization (CK: no fertilizer; NPK: mineral fertilizers; NPKS: mineral fertilizers plus straw). During the 60-day incubation period, a total of 524 bacterial OTUs and 72 fungal OTUs, which utilized straw-derived carbon, were identified and were found to be primarily distributed in the bacterial phyla of Proteobacteria, Actinobacteria and Bacteroidetes, and the fungal class of Sordariomycetes within Ascomycota. The three fertilized soils exhibited distinct straw-utilizing microbial communities along the decomposition process, in which key bacterial taxa (Flavobacterium , Nocardioides , Pseudomonas , Pseudoxanthomonas , Agromyces and Herpetosiphon) and key fungal taxa (Pleosporaceae , Lasiosphaeriaceae and Chaetomiaceae) exhibited significantly positive relationships with extracellular enzymes activities, thereby accelerating the straw decomposition process. Furthermore, due to higher nutrient availability, microbes can rapidly respond to straw addition, therefore, more bacteria and fungi, which are referred to as rapid responders, were identified in NPK and NPKS soils, relative to CK soils. Hierarchical and variation Partitioning (HP) analysis revealed a strong potential impact of multiple edaphic factors in shaping the microbial community to utilize the straw-derived carbon. N resources (NO 3 −-N and TN) and β-glucosidase were found to be significantly positively correlated with microbial utilizers' community. In conclusion, our findings elucidate the processes of establishment of microbial community and straw decomposition, as well as the association between microbial communities and edaphic factors under different long-term fertilization regimes. • Microbial utilizers of straw-derived C were identified using DNA-SIP approach. • Microbial utilizers communities were affected by fertilization and sampling time. • Key taxa in NPKS showed significantly positive relation with enzymes activities. • Microbes rapidly responded to straw addition under higher nutrient availability. • N resources and β-glucosidase were most related with microbial utilizers. [ABSTRACT FROM AUTHOR]

• Soil pH determines fertilization strategy and fungal community response. • Long-term inorganic fertilization can achieve high crop yield in alkaline soils. • Acidic soil productivity can be maintained by inorganic-organic fertilization. • Mortierella and Pseudaleuria were enriched by inorganic-organic fertilization. Agricultural fertilization plays a crucial role in crop production, and the fungal communities catalyze transformation of soil nutrients in support of crop production. However, it remains controversial about the optimal strategy for fertilizer inputs and the adaptive mechanisms of fungal communities across China. By using seven long-term field fertilization experiments in China, we analyzed crop yields, soil properties and fungal communities in soils that were treated for > 25 years with no fertilizer (control), inorganic fertilizers (NPK) and organic-inorganic fertilizers (NPKM). Long-term NPK resulted in significant acidification up to a decline by 1.20 pH units, while NPKM prevented acidification and increased pH up to 6.39 in three acidic soils with pH < 5.70. NPKM increased crop yields by 1.19–8.72 folds in acidic soils, being significantly higher than NPK. Specific saprotroph Mortierella and Pseudaleuria in acidic soils were exclusively enriched by NPKM. Soil pH was directly related to the abundance of Mortierella , and the enrichment of Mortierella species further caused a positive direct effect on crop yield. In four alkaline soils with pH > 8.11, both NPK and NPKM led to only marginal decline of soil pH, and NPK and NPKM showed comparable crop yields. Some members of Ascomycota in alkaline soils were both enriched by NPKM and NPK. Soil available P and C:N ratio, rather than pH, directly or indirectly affect crop yield in alkaline soils. High crop yield can be achieved by the sole use of inorganic fertilizers in alkaline soils, but acidic soil productivity should be maintained by organic amendment to counteract acidification by inorganic fertilization. Our study advances a mechanistic understanding for optimizing fertilization strategies towards sustainable agriculture under increasingly intensified fertilizer inputs. [ABSTRACT FROM AUTHOR]